package nachos.threads;

import nachos.machine.*;
import java.util.LinkedList;

/**
 * An implementation of condition variables that disables interrupt()s for
 * synchronization.
 *
 * <p>
 * You must implement this.
 *
 * @see	nachos.threads.Condition
 */
public class Condition2 {

    private Lock conditionLock;
    private LinkedList<KThread> so1_waitingThreads = new LinkedList<KThread>();

    /**
     * Allocate a new condition variable.
     *
     * @param	conditionLock	the lock associated with this condition variable.
     * The current thread must hold this lock whenever it uses <tt>sleep()</tt>,
     * <tt>wake()</tt>, or <tt>wakeAll()</tt>.
     */
    public Condition2(Lock conditionLock) {
        this.conditionLock = conditionLock;
    }

    /**
     * Atomically release the associated lock and go to sleep on this condition
     * variable until another thread wakes it using <tt>wake()</tt>. The current
     * thread must hold the associated lock. The thread will automatically
     * reacquire the lock before <tt>sleep()</tt> returns.
     */
    public void sleep() {
        Lib.assertTrue(conditionLock.isHeldByCurrentThread());

        conditionLock.release();

        so1_waitingThreads.add(KThread.currentThread());
        KThread.currentThread().sleep();

        conditionLock.acquire();
    }

    /**
     * Wake up at most one thread sleeping on this condition variable. The
     * current thread must hold the associated lock.
     */
    public void wake() {
        Lib.assertTrue(conditionLock.isHeldByCurrentThread());
        
        KThread so1_current;
        if (!so1_waitingThreads.isEmpty()) {
            so1_current = so1_waitingThreads.pop();
            so1_current.ready();
        }
    }

    /**
     * Wake up all threads sleeping on this condition variable. The current
     * thread must hold the associated lock.
     */
    public void wakeAll() {
        Lib.assertTrue(conditionLock.isHeldByCurrentThread());
        
        while (!so1_waitingThreads.isEmpty()) {
            wake();
        }
    }
}
